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Middle atmosphere Circulation

Atmospheric circulation affects climate through the transport of climate relevant trace gases and through dynamical coupling: Variability in the stratospheric circulation can influence temperature and precipitation extremes at the Earth surface.

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The large-scale circulation of the middle atmosphere is characterized by fast zonal winds and a much slower meridional circulation, with upward motion across the tropical tropopause and a poleward and downward motion in the stratosphere.

Climate models predict an acceleration of the middle atmosphere circulation over recent and coming decades due to changes in greenhouse gases and ozone-depleting substances, but existing observations do not provide a clear picture. Better understanding of the processes driving the stratospheric circulation and variability now and in the changing climate is therefore of high importance.

The current gap in our understanding of changes in the middle atmosphere circulation is summarized in this figure: Observations show a long-term decrease in the speed of the stratospheric Brewer-Dobson circulation with increasing age-of-air, while climate models show a significant increase in the speed, with decreasing age-of-air in the stratosphere.

Image credit: WMO 2022 Ozone Assessment